Photographs, both monochrome and color, can be captured and displayed through two side-by-side images that emulate human stereoscopic vision. While known colloquially as “3-D” photography, the more accurate term is stereoscopy. Such cameras have long been realized by using film, and more recently in digital electronic methods (including cellphone cameras).
Stereoscopy (also called stereoscopics or 3D imaging) is a technique for creating or enhancing the illusion of depth in an image by means of stereopsis for binocular vision. The word stereoscopy derives from the Greek “στερεός” (stereos), “firm, solid” + “σκοπέω” (skopeō), “to look”, “to see”.
Most stereoscopic methods present two offset images separately to the left and right eye of the viewer. These two-dimensional images are then combined in the brain to give the perception of 3D depth. This technique is distinguished from 3D displays that display an image in three full dimensions, allowing the observer to increase information about the 3-dimensional objects being displayed by head and eye movements.
Stereoscopy creates the illusion of three-dimensional depth from given two-dimensional images. Human vision, including the perception of depth, is a complex process which only begins with the acquisition of visual information taken in through the eyes; much processing ensues within the brain, as it strives to make intelligent and meaningful sense of the raw information provided. One of the very important visual functions that occur within the brain as it interprets what the eyes see is that of assessing the relative distances of various objects from the viewer, and the depth dimension of those same perceived objects. The brain makes use of a number of cues to determine relative distances and depth in a perceived scene, including:
Accommodation of the eye
Overlapping of one object by another
Subtended visual angle of an object of known size
Linear perspective (convergence of parallel edges)
Vertical position (objects higher in the scene generally tend to be perceived as further away)
Haze, desaturation, and a shift to bluishness
Change in size of textured pattern detail
Anatomically, there are 3 levels of binocular vision required to view stereo images:
1. Simultaneous perception
2. Fusion (binocular ‘single’ vision)
These functions develop in early childhood. Some people who have strabismus disrupt the development of stereopsis, however orthoptics treatment can be used to improve binocular vision. A person’s stereoacuity determines the minimum image disparity they can perceive as depth. It is believed that approximately 12% of people are unable to properly see 3D images, due to a variety of medical conditions. According to another experiment up to 30% of people have very weak stereoscopic vision preventing them from depth perception based on stereo disparity. This nullifies or greatly decreases immersion effects of stereo to them.
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